Geoscience Reference
In-Depth Information
Figure 24.3. Abandoned homesteads on the Alashan Plateau, Inner Mongolia, north-
ern China. Accelerated erosion followed a sudden increase in the human and animal
population in the 1950s as a result of migration from the south.
(Williams,
2000
a). These are probably reasonable order of magnitude estimates, given
the lack of accurate soil and vegetation maps against which to assess them.
Discussion with farmers and herdsmen before the drought broke in August
1999 revealed widespread concern over a perceived increase in sand and dust storms
and a decline in pasture quality (Williams,
2000
a). There was abundant and unambigu-
ous evidence of accelerated soil erosion by wind and water since the 1950s. Former
agricultural settlements immediately west of the rugged and wooded Helan Shan range
have been abandoned (
Figure 24.3
), and the adjacent fine-grained alluvial soils have
been severely gullied. In some places, only a single tree remains as a witness to the
riparian woodland of the 1950s.
Of even greater concern was the reactivation of previously stable and vegetated
dunes to the north and west of the mountains as a result of overgrazing by goats
and sheep. Monitored rates of dune advance amounted to more than 10 m/year near
the Yellow River to less than 1 m/year further inland. Along an 80 km reach on
the left bank of the Yellow River, opposite the industrial city of Wuhai, the dunes
were advancing at rates of up to 10 m/year. An estimated 80 million m
3
of sand is
being blown into the river each year in this sector. Major reafforestation of the mobile
